<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
<script>


    var EARTH_RADIUS = 6378137.0;    //单位M
    var PI = Math.PI;

    function getRad(d){
        return d*PI/180.0;
    }

    function getFlatternDistance(lat1,lng1,lat2,lng2){

        var f = getRad((lat1 + lat2)/2);

        var g = getRad((lat1 - lat2)/2);

        var l = getRad((lng1 - lng2)/2);



        var sg = Math.sin(g);

        var sl = Math.sin(l);

        var sf = Math.sin(f);



        var s,c,w,r,d,h1,h2;

        var a = EARTH_RADIUS;

        var fl = 1/298.257;



        sg = sg*sg;

        sl = sl*sl;

        sf = sf*sf;



        s = sg*(1-sl) + (1-sf)*sl;

        c = (1-sg)*(1-sl) + sf*sl;



        w = Math.atan(Math.sqrt(s/c));

        r = Math.sqrt(s*c)/w;

        d = 2*w*a;

        h1 = (3*r -1)/2/c;

        h2 = (3*r +1)/2/s;



        return d*(1 + fl*(h1*sf*(1-sg) - h2*(1-sf)*sg));

    };

   var  kil =  getFlatternDistance(40.484991998000055,115.72965078900006,40.647086890418066,115.72965078900006);
   var  kils =  getFlatternDistance(40.484991998000055,115.72965078900006,40.484991998000055,116.0313448544386);

    console.log(kil);
    console.log(kils);

</script>
</body>
</html>